Advancements in biomass materials for electromagnetic interference (EMI) shielding: a comprehensive review

Effective electromagnetic interference (EMI) shielding materials are essential to protect sensitive electronics and ensure proper functionality. Traditional shielding materials, such as metals and carbon-based composites, have been widely used, but they often come with limitations in terms of cost, environmental impact, and weight. In response to these challenges, biomass materials have gained attention due to their sustainability, lightweight nature, and effective shielding properties. A research team from Nanjing Forestry University, led by Prof. Jing Luo, has provided a comprehensive overview of the current state of research on biomass materials as EMI shielding materials, highlighting their potential and the advancements made in enhancing their performance through specific treatments and modifications.

Biomass materials, which are derived from renewable resources such as wood, bamboo, and cellulose, offer a unique set of advantages for EMI shielding. These materials are lightweight, biodegradable, and abundant, making them an attractive alternative to traditional shielding materials. Additionally, biomass materials have inherent porosity and structural complexity, which can be exploited to enhance their ability to absorb and reflect electromagnetic waves. The porous structure of biomass materials allows for the scattering of electromagnetic waves, which helps to reduce their intensity as they pass through. Moreover, biomass materials can be modified by adding conductive fillers or undergoing surface treatments to further enhance their shielding capabilities. For instance, the incorporation of metal nanoparticles, carbon-based materials like graphene, or MXene—a class of two-dimensional materials—into biomass can significantly improve their conductivity and electromagnetic shielding performance.

Wood, in particular, has been extensively studied for its potential as an EMI shielding material. Due to its natural structure, wood is lightweight, durable, and readily available, making it an ideal candidate for shielding applications. Wood-based composites, which combine wood with conductive materials such as carbon nanotubes, graphene, or metals, have shown significant promise in improving shielding effectiveness. These composites take advantage of wood's natural porosity and the added conductive fillers to form a conductive network that enhances the material's ability to absorb and reflect electromagnetic waves. Research has shown that wood can be treated with metal coatings or impregnated with conductive fillers to create composites with excellent EMI shielding properties. For example, wood-based composites with copper or silver coatings have demonstrated remarkable shielding effectiveness, often surpassing traditional shielding materials in terms of cost-effectiveness and sustainability.

Bamboo is another biomass material that has gained attention for its potential in EMI shielding applications. Bamboo has a unique structure that is both strong and lightweight, making it an excellent material for shielding. Additionally, bamboo has a fast growth cycle, making it a highly renewable resource. Bamboo fibers can be combined with conductive materials to form composites that provide enhanced electromagnetic shielding. Similar to wood, bamboo can be metallized with nickel or copper to create a conductive network that improves its ability to block electromagnetic waves. The combination of bamboo's natural strength and the added conductive fillers results in a material that is both effective and sustainable. Research has also shown that bamboo-based composites can be engineered to achieve high shielding effectiveness, making bamboo an attractive alternative to traditional metals and carbon-based composites.

Cellulose, one of the most abundant biopolymers in nature, has also been explored for its potential in EMI shielding. Cellulose has several key advantages, including its biodegradability, renewability, and ease of modification. It can be easily processed into various forms, such as films, foams, and aerogels, which can be further enhanced by the addition of conductive fillers. The addition of materials like carbon nanotubes, graphene oxide, or MXene to cellulose significantly improves its conductivity and shielding performance. Research has demonstrated that cellulose-based composites, such as cellulose foam or cellulose nanofiber composites, can achieve high EMI shielding effectiveness while maintaining lightweight and flexible properties. These materials are particularly attractive for applications in wearable electronics, where flexibility and comfort are crucial.

Lignin, a complex biopolymer found in the cell walls of plants, has also shown promise as an EMI shielding material. Lignin's unique chemical structure, which contains numerous phenolic groups, allows it to interact with metal nanoparticles and carbon-based materials to form conductive networks. By combining lignin with conductive fillers such as carbon nanotubes or metal nanoparticles, researchers have created lignin-based composites with enhanced shielding performance. Lignin-based materials have the added advantage of being highly stable and resistant to thermal degradation, making them suitable for use in high-temperature environments. Furthermore, lignin is a byproduct of the paper and biofuel industries, which makes it a sustainable and low-cost material for EMI shielding applications.

The mechanisms behind the EMI shielding capabilities of biomass materials are primarily based on reflection, absorption, and multiple internal reflections of electromagnetic waves. When an electromagnetic wave encounters a shielding material, part of the wave is reflected off the surface, while the rest is absorbed by the material and converted into heat. The porous nature of biomass materials contributes to the scattering and absorption of electromagnetic waves, while the addition of conductive fillers enhances the material's ability to absorb and dissipate electromagnetic energy. For instance, conductive fillers such as graphene and carbon nanotubes form a conductive network that facilitates the movement of electrons, helping to absorb the electromagnetic waves. Moreover, the interaction between the material's surface and the incident electromagnetic waves can lead to polarization effects, which further enhance the shielding effectiveness.

Despite the promising properties of biomass-based EMI shielding materials, there are still challenges to overcome. One of the main challenges is the variability in the properties of raw biomass materials, which can affect the performance of the final composite. For example, the natural variability in the density, porosity, and structure of wood and bamboo can lead to inconsistencies in shielding performance. To address this issue, researchers are working on developing standardized methods for processing and characterizing biomass materials to ensure consistent quality and performance. Additionally, while biomass materials have excellent potential for EMI shielding, their mechanical properties, such as tensile strength and durability, may not always meet the demands of certain applications. Future research is needed to improve the mechanical properties of biomass-based composites and enhance their resistance to environmental factors like moisture and temperature.

Another challenge lies in the scalability of biomass-based EMI shielding materials. While laboratory-scale studies have shown promising results, there are still hurdles to overcome in terms of large-scale production and cost-effectiveness. The processing methods for biomass-based materials, such as impregnation and surface treatments, can be time-consuming and expensive. Researchers are exploring more efficient and cost-effective manufacturing techniques to make these materials commercially viable. Additionally, ensuring that biomass-based composites meet the required performance standards for various industries is essential for their widespread adoption.

In conclusion, biomass materials represent a sustainable and promising alternative to traditional EMI shielding materials. Their lightweight nature, biodegradability, and ease of modification make them ideal candidates for a wide range of applications, from consumer electronics to aerospace and medical devices. By incorporating conductive fillers and optimizing processing techniques, biomass materials can be engineered to provide high shielding effectiveness, comparable to or even surpassing traditional materials. As research in this field progresses, biomass-based EMI shielding materials hold the potential to revolutionize the way we protect electronic devices from electromagnetic interference while contributing to environmental sustainability. The continued development of these materials will likely lead to the creation of greener, more efficient, and cost-effective solutions for EMI shielding in the future.